A conventional electric steering column apparatus is disclosed, for example, in Japanese Patent No. 2647476. In this apparatus, since a steering wheel is arranged at desired axial position and vertical position, the arrangement is such that a tilt joint or a telescopic joint is provided and a tilt position or a telescopic position of the steering wheel can be adjusted by means of an actuator which comprises an electric motor and a screw mechanism. Then, there is also provided a switch mechanism by which the electric motor is operated only when a working force of a predetermined level or higher is applied in a predetermined direction of the steering wheel, so as to electrically adjust the tilt position or the telescopic position (axial position) of the steering wheel.
However, in the above-mentioned electric steering column apparatus, the tilt position or the telescopic position of the steering wheel can not be detected. It is important to detect the position of the steering wheel, in order to finely adjust or control the position of the steering wheel. When the position of the steering wheel is to be detected, a brush or a rotary encoder or a linear encoder using a variable resistance, or the like, is usually employed. However, with such means, accurate detection may not be obtained due to abrasion of contacts, etc., for a long term use.
Also in the above-mentioned electric steering column apparatus, a tilt actuator (that is, an actuator for adjusting the tilt position of the steering wheel) and a telescopic actuator (that is, an actuator for adjusting the telescopic position of the steering wheel) are different components separately provided, so that the number of the constituent parts for steering must be increased, which causes a decline of mass productivity, etc., of the actuator and necessity for selecting two kinds of actuators in assembling the steering apparatus, and, in consequence, hinders the reduction in the manufacturing cost and the assembling steps.
For example, the electric tilt steering apparatus is generally arranged such that a rod is extended or contracted through a worm gear by an electric motor provided on a lower steering column, and an upper steering column coupled to an end of this rod through a bracket is moved in an inclined manner, whereby an angle of inclination of the steering wheel is adjusted to a desired angle.
In an electric tilt steering apparatus of a so-called upper part rocking type disclosed, for example, in Japanese Utility Model Publication No. 5-29979, an upper steering shaft is rockably coupled to a lower steering shaft through a universal joint and an upper steering column is rockably coupled to a lower steering column through a pin, correspondingly thereto. An electric motor for extending or contracting a rod through a worm gear is mounted on the lower steering column, and an end of this rod is coupled to a bracket which is provided on the upper steering column. With such arrangement, the rod is extended or contracted by the electric motor to incline the upper steering column with respect to the lower steering column fixed to the car body, thereby adjusting an angle of inclination of the steering wheel.
On the other hand, in an electric tilt steering apparatus of a so-called lower part rocking type disclosed in PCT Japanese Phase Publication No. 7-506308, a steering column is arranged to be integrally inclined with the position of a universal joint provided in a lower part of a steering shaft, as a center of a tilt movement, while the steering column is arranged to be movable a little in the axial direction with no tilt center, such as a pin. Further, a bell crank which is rocked by an electric motor is coupled to this steering column, whereby the bell crank is rocked by driving the electric motor so as to incline the steering column. When this bell crank is rocked, an axial force is generated to move the steering column in the axial direction. However, since the steering column is arranged to be freely movable in the axial direction, this axial force can be absorbed.
However, in the electric tilt steering apparatus of the so-called upper part rocking type disclosed in the above-mentioned Japanese Utility Model Publication No. 5-29979, both the steering shaft and the steering column are divided into upper and lower parts, respectively, which is disadvantageous in terms of the manufacturing cost because of the increased number of the constituent parts.
Also, since the rod of the electric motor is arranged to support the upper steering column and the upper steering shaft, if a load (vibration) is input downward and toward a front part of the car from the steering wheel side, this load (vibration) in the vertical direction directly works upon the rod and the rod receives most of this load (vibration). For this reason, the rigidity of this rod is required to be very high, and measures for suppressing backlash which may caused by the vibration of the rod are required to be fully taken.
Further, in the electric tilt steering apparatus of the so-called lower part rocking type disclosed in PCT Japanese phase Publication No. 7-506308, since the steering column has no tilt center such as a pin, if a load (vibration) is input downward and toward a front part of the car from the steering wheel side, this load (vibration) in the vertical direction directly works upon the telescopic portion of the steering shaft and this telescopic portion receives most of this load (vibration). For this reason, in order to secure a smooth operation of this telescopic portion or to prevent backlash due to the vibration of the telescopic portion, full measures are required to be taken for the telescopic portion.